1. Field of the Invention
The present invention relates to a film deposition apparatus and a film deposition method for depositing a film on a substrate by carrying out plural cycles of supplying in turn at least two source gases to the substrate in order to form a layer of a reaction product.
2. Description of the Related Art
As a film deposition technique in a semiconductor fabrication process, there has been known a so-called Atomic Layer Deposition (ALD) or Molecular Layer Deposition (MLD). In such a film deposition technique, a first reaction gas is adsorbed on a surface of a semiconductor wafer (referred to as a wafer hereinafter) under vacuum and then a second reaction gas is adsorbed on the surface of the wafer in order to form one or more atomic or molecular layers through reaction of the first and the second reaction gases on the surface of the wafer; and such an alternating adsorption of the gases is repeated plural times, thereby depositing a film on the wafer. This technique is advantageous in that the film thickness can be controlled at higher accuracy by the number of times alternately supplying the gases, and in that the deposited film can have excellent uniformity over the wafer. Therefore, this deposition method is thought to be promising as a film deposition technique that can address further miniaturization of semiconductor devices.
Such a film deposition method may be preferably used, for example, for depositing a dielectric material to be used as a gate insulator. When silicon dioxide (SiO2) is deposited as the gate insulator, a bis (tertiary-butylamino) silane (BTBAS) gas or the like is used as a first reaction gas (source gas) and ozone gas or the like is used as a second reaction gas (oxidation gas).
In order to carry out such a deposition method, use of a single-wafer deposition apparatus having a vacuum chamber and a shower head at a top center portion of the vacuum chamber has been under consideration. In such a deposition apparatus, the reaction gases are introduced into the chamber from the top center portion, and unreacted gases and by-products are evacuated from a bottom portion of the chamber. When such a deposition chamber is used, it takes a long time for a purge gas to purge the reaction gases, resulting in an extremely long process time because the number of cycles may reach several hundred. Therefore, a deposition method and an apparatus that enable high throughput are desired.
There are two types of the ALD methods. First, the ALD method of the first type is explained, taking an example of using a film deposition apparatus having a wafer receiving portion that is fixed in an evacuatable reaction chamber and on which a wafer is placed.
(1) First, the wafer is transferred into the reaction chamber and placed on the wafer receiving portion. In this case, only one wafer may be placed (a single-wafer process), or plural wafers may be placed (a batch process).
(2) After the wafer(s) is placed on the wafer receiving portion, the reaction chamber is evacuated to vacuum and film deposition conditions are set during evacuation. Specifically, a temperature of the wafer receiving portion (wafer temperature) is set at a temperature suitable for the ALD, and a pressure in the reaction chamber is set at a pressure suitable for the ALD.
(3) After the film deposition conditions are set, a reaction gas A is supplied to the reaction chamber for a predetermined period of time.
(4) Then, supplying the reaction gas A is terminated, and the reaction gas A is evacuated from the reaction chamber, in order to reduce intermixture and reaction of the reaction gas A remaining in the reaction chamber and a reaction B to be subsequently supplied.
(5) The reaction gas B is supplied to the reaction chamber for a predetermined period of time.
(6) The reaction gas B is terminated, and evacuated from the reaction chamber in the same manner as the step (4). This is carried out in order to reduce intermixture and reaction of the reaction gas B remaining in the reaction chamber and the reaction B to be supplied again.
(7) The above steps (3) through (6) are repeated at a predetermined times.
(8) When a film thickness of the film deposited on the wafer reaches a predetermined value, all the reaction gases are stopped; a pressure of the reaction chamber is returned to an atmospheric pressure; and the wafer is transferred out from the reaction chamber.
The ALD method of the first type is advantageous in that the reaction gases A, B can be substantially prevented from being intermixed in the reaction chamber because the reaction chamber can be fully evacuated before supplying the reaction gases A, B. On the other hand, film deposition time is lengthened because this method includes steps of supplying the reaction gas A, evacuating the reaction gas A, supplying the reaction gas B, and evacuating the reaction gas B (namely, the reaction chamber needs to be evacuated to vacuum in order to avoid intermixture of the reaction gases A, B). In addition, because process controlling instruments such as valves and mass flow controllers used in a gas supplying system and valves in a gas evacuation system of the film deposition apparatus need to be opened and closed many times during the film deposition time, the process controlling instruments are subject to maintenance at relatively high frequency, which reduces utilization rate of the film deposition apparatus and productivity.
In order to reduce the film deposition time due to the time-consuming evacuation processes, thereby reducing the frequency of the maintenance of the process controlling instruments and improving the productivity, use of an ALD apparatus with a rotatable susceptor on which plural of the wafers are placed is considered, which is explained in the following as the ALD method of a second type.
A mini-batch type ALD apparatus with the rotatable susceptor is used in the second type. This apparatus includes a reaction chamber whose inside can be maintained at reduced pressures and a turntable rotatably provided in the reaction chamber. The turntable can hold as many wafers as desired depending on a size of the wafer to be processed and a diameter of the turntable.
In the ALD method of the second type,
(1) first, plural wafers are placed on the turntable in the reaction chamber;
(2) after the plural wafers are placed on the turntable, the reaction chamber is evacuated to vacuum, the turntable starts rotating, and the wafers are heated at a predetermined temperature;
(3) a separation gas is supplied at a predetermined flow rate to an area between reaction areas where corresponding reaction gases are supplied;
(4) when predetermined reaction gases are supplied at predetermined flow rates to upper surfaces of the wafers, the upper surfaces of the wafers are exposed alternatively to the reaction gases, thereby carrying out the ALD; and
(5) after a film having a predetermined thickness is obtained on each of the wafers, the reaction gases are stopped, the turntable stops rotating, and the inner pressure of the reaction chamber is returned to the atmospheric pressure.
The ALD method of the second type is advantageous in that the film thickness can be adjusted by the number of rotations of the turntable.
In addition, because supplying the reaction gases A, B and evacuating the reaction gases A, B are carried out at the same time, the number of ON/OFF operations of the process controlling instruments is reduced and thus the process controlling instruments are subject to maintenance at relatively low frequency, which may increase utilization rate of the film deposition apparatus and productivity.
In the ALD method of the second type, plural areas where the corresponding reaction gases are supplied and an area where the reaction gases are evacuated are required in the reaction chamber. In order to avoid intermixture of the reaction gases in the reaction chamber, it can be easily understood that independent reaction areas (compartments) should be created by partition walls. However, bottom ends of the partition walls need to be as close to the turntable as possible in order to sufficiently avoid gaseous communication between the reaction areas. Alternatively, the turntable needs to be intermittently rotated. Namely, the reaction areas are enclosed so that the turntable is raised to contact the partition walls via a sealing member therebetween, and the wafers on the turntable are exposed to the reaction gas in the corresponding enclosed reaction area. In this method, the turntable cannot be continuously rotated, which may increase the film deposition time.
Therefore, a mechanism is required for separating the reaction gases in order to alternatively expose the upper surfaces of the wafers to the reaction gases while avoiding the intermixture of the reaction gases even when the turntable is rotated at higher rotation speed.
Patent Document 1 discloses a method of evacuating reaction gases along with a separation gas through an evacuation opening provided at an upper portion of the reaction chamber between an ejection opening of the separation gas and an area where a reaction gas is supplied.
Patent Document 2 discloses a method of separating the reaction gases by use of air-curtain effect while a wafer supporting member is rotated.
Patent Document 3 discloses a method of rotating a wafer receiving member having a partition wall and a slanted surface where a wafer is placed so that the wafer on the slanted surface can cope with the centrifugal force due to the rotation of the wafer receiving member, so that the wafer passes through process areas and evacuation areas.
Patent Document 4 discloses a method of depositing a film by alternately ejecting two reaction gases.
Patent Document 5 discloses a method of supplying a source reaction gas from a rotatable nozzle to a reaction area including a vacuum evacuation opening and purging the source reaction gas by the rotatable nozzle.
In a film deposition apparatus and film deposition method disclosed in Patent Document 6 (7, and 8), after a source gas (or a reaction gas) is supplied to an area where a wafer is placed, an environment of the area is purged with a purge gas by use of a separation gas nozzle.
Patent Document 9 discloses a turntable on which plural wafers are placed, plural supplying zones (or supplying opening) from which corresponding reaction gases are supplied and that are provided at circumferential intervals, and two evacuation zones (or evacuation opening) provided along the circumferential direction between the plural supplying zones.
Patent Document 10 discloses a clamp ring that fixes a wafer placed in a wafer receiving area of a susceptor (or platen) in order to avoid wafer damage or breakage that may be caused when centrifugal force due to rotation of the susceptor forces the wafer to hit an inner side wall of the wafer receiving area.
Patent Document 1: U.S. Pat. No. 7,153,542 (FIGS. 6(a), 6(b))
Patent Document 2: Japanese Patent Application Laid-Open Publication No. 2001-254181 (FIGS. 1 and 2)
Patent Document 3: Japanese Patent Publication No. 3144664 (FIGS. 1 and 2, claim 1)
Patent Document 4: Japanese Patent Publication Laid-Open Publication No. H04-287912
Patent Document 5: U.S. Pat. No. 6,634,314
Patent Document 6: Japanese Patent Publication Laid-Open Publication No. 2007-247066 (paragraphs 0023 through 0025, and 0058, FIGS. 12 and 18)
Patent Document 7: U.S. Patent Application Publication No. 2007/218701
Patent Document 8: U.S. Patent Application Publication No. 2007/218702
Patent Document 9: Published Japanese Translation of PCT International Publication No. 2008-516428 (or corresponding U.S. Patent Publication No. 2006/0073276)
Patent Document 10: Japanese Patent Application Laid-Open Publication No. H09-115994 (FIGS. 4, 6, and 7)